Nuclear magnetic resonance method quantifying fractures in unconventional source rocks

Abstract

A method for analyzing unconventional rock samples using nuclear magnetic resonance (NMR), tracking fluid change in the rock sample over a time period, calculating transverse relaxation time (T2) generating fluid distribution profiles by the computer processor and based on a NMR imaging, where the fluid distribution profiles representing a movement of the fluid, and obtaining, quantification of fracture volume by the computer processor and based on the NMR imaging.

What is claimed is: 
     
       1. A method for analyzing unconventional rock samples, the method comprising:
 introducing fluid to a rock sample; 
 acquiring, by a computer processor, nuclear magnetic resonance (NMR) measurements of the rock sample to track fluid change in the rock sample; 
 calculating transverse relaxation time (T 2 ) based on the NMR measurements; 
 generating, by the computer processor and based on an NMR imaging, fluid distribution profiles, the fluid distribution profiles representing a movement of the fluid; and 
 obtaining, by the computer processor and based on the NMR imaging, a quantification of fracture volume, the quantification of the fracture volume representing an amount of fluid in a fracture. 
 
     
     
       2. The method of  claim 1 , further comprising:
 identifying a presence of fractures in the rock sample by measuring movement of the fluid through the rock sample over time; 
 predicting an extent of the fractures in the rock sample by determining fluid distribution profiles of the fluid; and 
 quantifying the fracture volume through a measurement of at least one fracture fluid peak in an NMR spectrum. 
 
     
     
       3. The method of  claim 1 , wherein the rock sample is dried in vacuum before acquiring NMR measurements. 
     
     
       4. The method of  claim 1 , wherein the fluid is introduced to the rock sample on one end, using a spontaneous imbibition. 
     
     
       5. The method of  claim 1 , wherein the NMR imaging is obtained at time intervals to track spatial and temporal changes in the rock sample. 
     
     
       6. The method of  claim 1 , wherein the transverse relaxation time (T 2 ) is obtained from a decay due to surface relaxation and bulk relaxation. 
     
     
       7. The method of  claim 1 , wherein a Carr Purcell Meiboom Gill (CPMG) sequence is used to acquire NMR imaging at different imbibition time. 
     
     
       8. The method of  claim 1 , wherein the fracture volume is obtained through a measurement of peak volumes by calculating an area under the curve in NMR T 2  spectra. 
     
     
       9. A computer system for analyzing unconventional rock samples, comprising:
 a processor; and 
 a memory coupled to the processor, the memory storing instructions, when executed,
 comprising functionality for: 
 acquiring nuclear magnetic resonance (NMR) measurements of a rock sample; 
 generating, based on NMR imaging, fluid distribution profiles, the fluid distribution profiles representing a movement of the fluid in the rock sample; and 
 obtaining, based on NMR imaging, a quantification of fracture volume, the quantification of the fracture volume representing the amount of the fluid in a fracture of the rock sample. 
 
 
     
     
       10. The computer system of  claim 9 , further comprising:
 identifying a presence of fractures in a rock sample by measuring movement of fluid through the rock sample over time; 
 predicting an extent of the fractures in the rock sample by determining fluid distribution profiles of the fluid; and 
 quantifying the fracture volume through a measurement of peak volumes in NMR spectra. 
 
     
     
       11. The computer system according to  claim 9 , further comprising:
 generating, by inversion of the NMR measurements, a spatial transverse relaxation time (T 2 ) distribution; and 
 generating, based on the spatial T 2  distribution, a saturation profile representing distribution of the fluid stored in the rock sample. 
 
     
     
       12. The computer system of  claim 11 , wherein a NMR saturation profile may be obtained, by a computer processor and based on NMR imaging, using SPRITE DHK sequence. 
     
     
       13. The computer system of  claim 11 , wherein the location of the fluid is determined by examining the y-axis of the saturation profile plot. 
     
     
       14. The computer system of  claim 9 , wherein NMR imaging is obtained at time intervals to track spatial and temporal changes in the rock sample. 
     
     
       15. The method of  claim 9 , wherein the T 2  is obtained from a decay due to surface relaxation and a bulk relaxation. 
     
     
       16. The computer system of  claim 9 , wherein Carr Purcell Meiboom Gill (CPMG) sequence may be used to acquire NMR imaging at different imbibition time. 
     
     
       17. The computer system of  claim 9 , wherein the fracture volume is obtained through a measurement of peak volumes by calculating area under the curve in NMR T 2  spectra. 
     
     
       18. A non-transitory computer readable medium storing instructions executable by a computer processor for analyzing unconventional rock samples, the instructions, when executed by the computer processor, comprising functionality for:
 acquiring nuclear magnetic resonance (NMR) measurements of the rock sample; 
 generating, based on NMR imaging, a fluid distribution profiles, the fluid distribution profiles representing a movement of a fluid front; and 
 obtaining, based on NMR imaging, a quantification of fracture volume, the quantification of the fracture volume representing the amount of the fluid in a fracture. 
 
     
     
       19. The non-transitory computer readable medium of  claim 18 , further comprising:
 identifying a presence of fractures in a rock sample by measuring movement of fluid through the rock sample over time; 
 predicting an extent of the fractures in the rock sample by determining fluid distribution profiles of the fluid; and 
 quantifying the fracture volume through a measurement of peak volumes in NMR spectra. 
 
     
     
       20. The non-transitory computer readable medium according to  claim 18 , further comprising:
 generating, by inversion of the NMR measurements, a spatial transverse relaxation time (T 2 ) distribution; and 
 generating, based on the spatial T 2  distribution, the saturation profile representing distribution of the fluid stored in the rock sample.